W. Mark Felt Sr., the associate director of the FBI during the Watergate scandal who, better known as "Deep Throat," became the most famous anonymous source in American history, died yesterday. He was 95.

Felt died at 12:45 p.m. at a hospice near his home in Santa Rosa, Calif. where he had been living since August.

Felt "was fine this morning" and was "joking with his caregiver," according to his daughter, Joan Felt. She said in a phone interview that her father ate a big breakfast before remarking that he was tired and went to sleep.

"He slipped away," she said.

As the second-highest official in the FBI under longtime director J. Edgar Hoover and interim director L. Patrick Gray, Felt detested the Nixon administration's attempt to subvert the bureau's investigation into the complex of crimes and coverups known as the Watergate scandal that ultimately led to the resignation of President Richard M. Nixon.

He secretly guided Washington Post reporter Bob Woodward as he and his colleague Carl Bernstein pursued the story of the 1972 break-in at the Democratic National Committee's headquarters at the Watergate office building, and subsequent revelations of the Nixon administration's campaign of spying and sabotage against its perceived political enemies.

Felt insisted on remaining completely anonymous, or on "deep background." A Post editor dubbed him "Deep Throat," a bit of wordplay based on the title of a pornographic movie of the time. The source's existence, but not his identity, became known in Woodward and Bernstein's 1974 book, "All the President's Men," and in the subsequent movie version, in which actor Hal Holbrook played the charismatic but shadowy source.

Felt, a dashing figure with a full head of silver hair, an authoritative bearing and a reputation as a tough taskmaster, adamantly denied over the years that he was Deep Throat, even though Nixon suspected him from the start.

It wasn't until May 30, 2005, that Felt's family revealed his identity in an article for Vanity Fair magazine. The article, written by San Francisco lawyer John D. O'Connor, did not make clear why Felt, suffering from dementia, admitted his identity after more than 30 years. Woodward confirmed the revelation, and the secret was finally out.

No one knows exactly what prompted Felt to leak the information from the Watergate probe to the media. He was passed over for the post of FBI director after Hoover's 1972 death, a crushing career disappointment. But by the time he told O'Connor, "I'm the guy they used to call Deep Throat," he was enfeebled by a stroke, and his memory of the era had almost completely vanished because of Alzheimer's disease.

Felt, who saw all the FBI investigative paperwork, was acquainted with Woodward from a chance meeting at the White House in 1969 when Woodward was still in the Navy.

It took many newspaper stories, a House and Senate investigation, the revelation of a secret tape recording system in the Oval Office, the firing of a special prosecutor, the opening of articles of impeachment and the discovery of a "smoking gun" tape recording before Nixon resigned on Aug. 9, 1974.